This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-367027 filed on Dec. 1, 2000.
The present invention relates to an ion current detection system and method for an internal combustion engine.
Conventionally, a combustion status detection system is proposed to detect an ion current generated by combustion and detect accurately a combustion status such as misfire, knocking or the like on a basis of the current. In the system, the ion current generated when a low voltage that almost causes a spark is impressed after a spark is detected. A predetermined essential signal is extracted from the ion current to determine knocking and misfire. However, the proposed system requires a power supply dedicated to the ion current detection.
Besides, a residual magnetism in an ignition coil after a spark causes a noise and lowers the detection accuracy of the ion current. To evade the influence of the noise, the ion current detection ought to be started after the noise attenuates enough. Therefore, there is a possibility that the time period available for the ion current detection is too short to complete the detection at high engine speed or the like.
The present invention is made in view of the problems described above and the object thereof is to provide an ion current detection system and method that enables an accurate ion current detection with a simple system configuration for an internal combustion engine.
A battery, an energy charge inductance, and a first transistor are connected in series in an ignition system. A primary winding and a second switching device are connected in series between the ground and a point between the energy charge inductance and the first switching device. A drive circuit switches periodically on and off the first switching device and the second switching device during multispark duration of the spark plug such that each switching device has a different switching status from each other.
After the multispark duration, the drive circuit switches periodically on and off the second transistor with a shorter interval than that in the multispark duration while holding the first transistor switched off. The switching interval is set to generate such a small energy discharge every switching interval that a relatively low voltage that almost causes a spark is impressed to the spark plug. Ion current detection is implemented by using this voltage as a power source. The voltage is impressed to the spark plug by switching on and off the second transistor after the multispark duration of the plug so that an extra power source dedicated to the ion detection is not required, and thereby the configuration of the system is simplified. In addition, the switching of the second transistor is started right after the multispark duration so that magnetism at the ignition coil and a residual charge at the plug, which are generated due to a spark, are eliminated immediately. Therefore, the ion current detection is not interfered by magnetic noise.